1. Field of the Disclosure
This disclosure relates generally to catalyst systems and more particularly to a method for selecting the layer in which a Cu—Mn spinel structure active phase may be applied to enhance performance of ZPGM catalyst systems for TWC application.
2. Background Information
Internal combustion engines produce exhaust gases having compositions that oscillate over time between air/fuel ratios that are slightly rich of stoichiometric, and ratios that are slightly lean of stoichiometric. However, a common problem among conventional active phase catalysts may be related to NO and CO conversion efficiency, which may fall very rapidly when the engine is operated outside of that band of air/fuel ratios. Under lean engine operations, there is excess oxygen and the reduction of NOx is not favored. Under rich conditions, the excess of fuel consumes all of the available oxygen prior to the catalyst.
Common three way catalysts (TWC) may work by converting carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful compounds or pollutants. A lack of sufficient oxygen may occur either when oxygen derived from NOx reduction is unavailable, or when certain maneuvers such as hard acceleration enrich the mixture beyond the ability of the converter to supply oxygen, as the TWC catalyst deteriorates because of aging, its ability to store oxygen diminishes, and the efficiency of the catalytic converter decreases.
Recent environmental concerns for a catalyst's high performance have increased the focus on the operation of a TWC catalyst at the end of its lifetime. Catalytic materials used in TWC applications have also changed, and the new materials requires being thermally stable under the fluctuating exhaust gas conditions.
Consequently, prior art TWC catalyst preferably use platinum group metal (PGM), which in turn drives up their cost and therefore the cost of catalysts applications. Accelerated catalyst reaction and enhanced performance is desirable, which is particularly important for meeting increasingly stringent state and federal government vehicle emissions standards. Therefore, there is a continuing need to provide cost effective catalyst systems that is free of PGM (ZPGM) and can provide sufficient conversion so that HC, NOx, and CO emission standards can be satisfied.
For the foregoing reasons, there is a need of selecting a layer for applying ZPGM active phase in washcoat, or in overcoat, which may produce an optimized TWC catalyst systems, employing a formulation substantially free of PGM and RE metals for washcoat or overcoat catalyst compositions, capable to achieve similar or better performance in TWC condition.